Turbochargers that are used on both diesel and gasoline engines to increase power output and reduce fuel consumption are becoming more and more prevalent in the marketplace since they also contribute to lowering exhaust emissions. They will be a significant factor in meeting the federally mandated mileage and emission standards that must be met by 2016.
Engines that are required to produce high power and high torque at low engine speeds, diesel truck engines for example, or passenger car engines that need to accelerate rapidly, require turbochargers that are capable of supplying high charge air pressure at low engine speeds, up to the torque peak speed of the engine. Above the torque peak speed, turbochargers with waste gates have been employed to prevent the turbocharger from exceeding its speed limit, and to maintain the charge air pressure constant over the high engine speed range. Turbochargers with waste gates are in common use today to bypass exhaust gas around the turbocharger turbine wheel to limit the speed of the turbocharger rotor and hold the boost pressure constant.
A predetermined maximum boost pressure generated by the turbocharger compressor is used to open the waste gate valve that is usually built into the hot turbocharger turbine casing. The waste gate valve and its operating mechanism represent a significant cost addition to the turbocharger.
Some turbochargers used on gasoline engines are subjected to higher exhaust gas temperatures than those used on diesel engines and require a cooling jacket in the bearing housing to protect their internal components from excessive heat. Currently, the cooling medium is engine coolant that must be piped from the engine to the turbocharger at its location within the engine enclosure and returned to the engine cooling system from the turbocharger cooling jacket.
Dr. William E. Woollenweber's patent application Ser. No. 12/803,618, titled “Air-Cooled Turbocharger with Optional Internal Pressure Relief Valve”, discloses a turbocharger that uses compressed air from the engine air intake system to cool the turbocharger, thus eliminating the need for engine coolant and its accompanying piping to and from the turbocharger. One embodiment of the air cooling system uses a spring-loaded valve mounted downstream of an air-to-air aftercooler in the air intake system of the engine that limits the boost pressure to the engine to a predetermined value, and the air that is taken from the intake manifold is piped to the cooling jacket of the turbocharger to cool its internal parts. The use of a waste gate is thereby eliminated.